1. Field of the Invention
This invention relates to a method for forming a light waveguide by use of polymer material, and it is usable for various light waveguide, optical integrated circuit, and optical wiring board to be used in general optical field, micro optical field, optical communication field, and optical information processing field.
2. Description of the Related Art
Inorganic material such as quartz, glass, and oxide ferroelectric material, and polymer material have been used for forming a light waveguide. Among these materials, polymer material is suitable for forming a light waveguide having a large area because polymer material is easy to be formed in the thin film configuration by means of spin coat technique and dip technique in comparison with inorganic material. Furthermore, according to this method, polymer material is advantageous in that a light waveguide can be formed on a substrate that is difficult to be subjected to high temperature heat treatment such as a semiconductor substrate and plastic substrate in the case where polymer material is used because a film can be formed without high temperature heat treatment when the film is formed, differently from the case where inorganic glass such as quartz is used. Furthermore, a flexible light waveguide can be formed because of the flexibility and resiliency of polymer material. On the reason described hereinabove, it is expected that the light waveguide parts such as optical integrated circuit used in the optical communication field and optical wiring board used in the optical information processing field is mass-produced at low cost by use of optical polymer material.
It is said that the optical polymer material is problematic in the environmental resistance such as heat resistance and humidity resistance, but such problematic properties of the optical polymer material have been improved recently. Furthermore, a method in which photosensitive polymer or resist is used is very simple and excellent in mass-productivity.
However, because polymer material that is solid at a room temperature has been used as photosensitive material heretofore, a thick film formed of polymer material causes scattering seriously in the ultraviolet region and visible region to result in poor light transmittance. As the result, the reliability of a pattern of a thick film is low particularly and results in poor resolution when the polymer material is hardened. These disadvantages are reflected adversely on the loss of a light waveguide formed of polymer material. Furthermore, because the absorption loss of the material is not improved and the transparency has remained poor, the waveguide loss is high disadvantageously. On the reason described hereinabove, the optical parts formed of such photosensitive material is insufficient to be used practically.
To solve the abovementioned problem, a method in which a pattern is formed by use of liquid photoresist instead of polymer material that is solid in the room temperature has been proposed. However, because such material is fluid, the thickness of a coated film is changed after coating of the resin and the change does not allow the film to be formed reproducibly and controllably. Furthermore, the method in which photosensitive material is used requires complex process such as etching, and hazardous alkaline waste liquid is generated in the process, and a large number of processes are required.
On the other hand, the inventors of the present invention proposed a method for forming an image and a method for manufacturing color filter previously in which electrodeposition material containing coloring material is electrically deposited or photoelectrically deposited by applying a low voltage to form an image excellent in resolution. The invention is disclosed in detail in Japanese Published Unexamined Patent Applications No. Hei 10-119414, No. Hei 11-189899, No. Hei 11-105418, No. Hei 11-174790, No. Hei 11-133224, and No. Hei 11-335894. The method for forming an image and the method for manufacturing color filter is characterized in that a color film excellent in resolution is formed by means of a simple method, and this technique is applied mainly in the field of the display device such as liquid crystal display device.
On the other hand, the light waveguide is a technique used in the field of the optical communication that is different from the field of the display device. The light waveguide is formed from dielectric material or photosensitive material by means of fine working through complex processes including photolithography. A method for forming a light waveguide by means of electrodeposition technique without complex processes such as photolithography has not been proposed.